The present invention is directed to a chemically modified clay that was rendered organophilic, and has a charged surface, and to methods for its use. This charged organophilic clay is useful in the removal of charged contaminants, both positive and negative, both organic and inorganic, from water. This method is particularly useful in the treatment of wastewater, surface water and ground water.
Removal of cationic heavy metals from water is well established in industry. Media that have been in use for years are bentonite (smectite), zeolite, and cation exchange resins. These media remove heavy metals such as Pb, Zn, Ni, Co, Cd, etc., by ion exchange, meaning the major cation present at the surface of the media, usually Na, Ca, Mg, is replaced by heavy metal cation present in the water because those ions are easily released by the clay. The exchanged ion becomes part of the contaminant load of the water.
None of these methods, however, are able to remove negatively charged organic compounds such as humic and fulvic acids. While these compounds, by definition, are acids, they do have negative charges spread throughout their structure.
None of these methods are capable of removing inorganic, negatively charged compounds such as the chromate, selenite and arsenate anions from water. Furthermore, none of these methods are able to remove positively charged organic compounds such as chelating agents, amines and cationic surfactants from water.
Organoclays have been used in the past for removal of non-polar oily substances by partitioning. The following relevant U.S. patents apply: U.S. Pat. No. 2,367,384 to Tymstra; U.S. Pat. No. 2,937,142 to Rios; U.S. Pat. No. 4,473,477 to Beall; U.S. Pat No. 4,517,094 to Beall.
None of these aforementioned methods suggests the use of charged organoclays for removal of positively or negatively charged contaminants. None of these methods suggest the use of charged organoclays for the removal of inorganic anionic metals such as arsenate, selenite and chromate. Organoclays mentioned in the Beall patents are non-ionic. In fact, patent U.S. Pat. No. 4,517,094 discloses that lower molecular weight/higher solubility compounds pass through columns filled with non-ionic organoclays.
On the other hand, activated carbon has long been used to remove such compounds as humic and fulvic acids and chelates such as EDTA. However, the humic acids are very large and foul activated carbon quickly. Non-ionic organoclays are also of much lower capacity. The kinetics of activated carbon for chelates are so slow that activated carbon is not effective for such compounds.